1. Field of the Invention
The present invention relates to the field of display technology, and in particular to a thin-film transistor (TFT) array substrate.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and thus have wide applications, such as liquid crystal televisions, mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens, making them take a leading position in the field of flat panel displays.
Most of the LCDs that are currently available in the market are backlighting LCDs, which comprise a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is that liquid crystal molecules are filled between a thin-film transistor (TFT) array substrate and a color filter (CF) substrate and a drive voltage is applied to the two substrates to control a rotation direction of the liquid crystal molecules in order to refract out light emitting from the backlight module to generate an image.
The TFT array substrate comprises a plurality of gate lines and data lines. The plurality of gate lines and the plurality of data lines are perpendicular to each other to define a plurality of pixel units. Each of the pixel units comprises therein a TFT, a pixel electrode, and a storage capacitor. The TFT has a gate electrode that is connected to the gate lines, a source electrode that is connected to the data lines, and a drain electrode that is connected to the pixel electrode. When the gate lines are driven, the TFT is set in a conducting state so that a grayscale voltage signal that is fed through the corresponding data line is loaded into the pixel electrode, whereby a corresponding electric field is generated between the pixel electrode and a common electrode. The liquid crystal molecules contained in the liquid crystal layer is acted upon by the electric field to change direction thereby achieving displaying of various images.
The storage capacitor provides an important function of maintaining a voltage level. An existing TFT array substrate is structured to form a storage capacitor by means of an overlapping portion between the common electrode and the pixel electrode. Referring to FIGS. 1-3, a conventional TFT array substrate generally comprises: a backing plate 10, a buffer layer 20 formed on the backing plate 10, a plurality of TFTs 90 formed on the buffer layer 20 and arranged in an array, a planarization layer 50 covering on the TFTs 90, a common electrode 60 formed on the planarization layer 50, a protection layer 70 covering the common electrode 60, and a patterned pixel electrode 80 formed on the protection layer 70. The pixel electrode 80 overlaps a portion of the common electrode 60 to form a storage capacitor Cst. The pixel electrode 80 is in connection with a drain electrode 901 of the TFT 90. The drain electrode 901 of the TFT 90 is in connection with a poly-silicon semiconductor layer 902. In the conventional TFT array substrate, the drain electrode 901 of the TFT 90 has a small area and is provided only for electrical connection with the pixel electrode 80 and the poly-silicon semiconductor layer 902. The drain electrode 901 does not overlap the common electrode 60.
With the continuous progress of the display technology, the definition and resolution of high quality display panels are getting increasingly high so that the aperture ratio of the display panels are correspondingly reduced and the storage capacitance is getting increasingly reduced. The charging time for each of the pixels is gradually shortened. The amount of charges retained in the storage capacitor is no longer capable of maintaining a normal operation voltage for the pixel and eventually, drawbacks, such as crosstalk and image sticking, result. Thus, it is an issue to be immediately addressed to expand the capacity of the storage capacitor of a high quality display panel. The conventional TFT array substrate shown in FIGS. 1 and 2 is generally hard to change the area of the patterned pixel electrode 80 due to limitations imposed by technical capability and desires for optic taste and transmission rate. In other words, it is not possible to expand the capacity of the storage capacitor by means of increasing the area of the pixel electrode 80.